System for determining the rate change of pressure

ABSTRACT

A rate of change of pressure detector employing an open loop circuit where the control nozzles of a proportional fluid amplifier are connected to a pressure source, whose rate of change of pressure is to be measured, by a pair of passages one of which is longer than the other. The pressure at the pressure source is differentiated to provide a pressure difference at the outlets of the pr

United States Patent [72] Inventor Robert H. Bellman 3,333,596 8/1967Bottone,.1r. 137/81.5 Horseheads,N.Y. 3,379,204 4/1968 Kelley et a1.137/81.5 [21] Appl. No. 676,803 3,413,996 12/1968 Fine 137/81.5 [22]Filed Oct. 20, 1967 3,474,959 10/1969 Katz l37/81.5X [45] Patented Jan.12, :71 k FOREIGN PATENTS 1 Asslgnee 5 1,002,089 8/1965 Great Britain137/815 a corporation of New York Primary Examiner-Samuel ScottAttorneys-Clarence R. Patty, Jr. and Walter S. Zebrowski [54] SYSTEM FORDETERMINING THE RATE CHANGE OF PRESSURE ABSTRACT: A rate of change ofpressure detector employing 7 Claims,4 Drawing Figs. an open loopcircuit where the control nozzles of a proportional fluid amplifier areconnected to a pressure source, [52] :LS. (g1 F whose mm of change ofpressure is to be measured, by a p 2 'f i .3 5 of passages one of whichis longer than the other. The pressure l l o are at the pressure sourceis differentiated to provide a pressure ['56] References Citeddifference at the outlets of the proportional fluid amplifier which is afunction of the rate of change of pressure of said UNITED STATES PATENTSpressure source in accordance with the equation 3,238,959 3/1966 Bowles137/815 3,159,168 12/1964 Readerm 137/815 AP =G K (Iia) 3,266,510 8/1966Wadey 137/815 P c I l I 1 I I I I I I I I ,,,,,,,,,J, B\,,.1

2 l2 1 20 l s D I PATENTED JAN 1 219m sum 1 or 2 11111111111IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIrIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII lIIIIIIIIlIIIlIIIIII/IjlIJIIIIIIIIIIIIIIIIII[III/IIII JIIIJIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIN A RM 0L TL WE We H T R E B o R III A ATTORNEY PATENTEU 12191;

SHEET 2 BF 2 O f fi I d! O i i -& I d? P- I K l 2 c t INVENTOR. ROBERTH. BELLMAN F lg BY M {W ATTORNEY noted disadvantages.

SYSTEM FOR DETERMINING THE RATE CIIANGE OF PRESSURE BACKGROUND OF THEINVENTION Heretofore known means for determining the rate of change ofpressure have been complicated, delicate, and expensive. One example ofprior art methods is as follows. Change of pressure was measured bypneumatic or fluidic means and then such fluidic'signals were convertedto electrical signals which were subsequently applied to an electricalcircuit or computer that differentiated them to provide rate of change.As is readily seen, such a system orlmethod is very-complicatedemploying costly equipment which was subject to damage or error inpractical applications.

Unlike an ordinarybistable lock-on" type fluid amplifier wherein thepower locks on to one wall or the other of an interaction chamber andthe power stream is directed substantially entirely to one or the otherof a pair of outlet passages in response to fluid signals applied to thecontrol nozzles thereof, a proportional fluid amplifier does not lock onto either wall and distributes or apportions the power stream betweenthe outlet passages in response to the pressure differential across thecontrol noules. A proportional fluid amplifier is therefore a fluidicanalogue device. Proportional fluid amplifiers may be either of thevent-type or center dump type. In either case, depending on thedifference in pressures applied to the control nozzles the power streammay be directed entirely to one outlet passage or the other,proportionedbe'tween them, or may be deflected beyond both and vented toambient. The gain of a proportional fluid amplifier is determined by theratio of the difference between the pressures within the outlet passagesto the difference of the pressures applied to the control nonles.

SUMMARY OF THE INVENTION The objects of the present invention are toprovide a simple, direct, rugged, and inexpensive means for. detenniningthe rate of change of pressure which overcomes the heretofore Accordingto the present invention, a system for detennining the rate of change ofpressure comprises a proportional fluid amplifier, one of the controlnoules of which is connected to the source of pressure to be sensed bymeans of a first passage intermediate said source and thecontrol'nozzle, while the other control nozzle of the proportional fluidampli fier is connected by means of a second passage to said pressuresource, the second passage being longer than the first passage. Thepressure difference AP, at the outlets of said proportional fluidamplifier is a function of the rate of change of 7 pressure of saidpressure source in accordancewith the equation the following detaileddescription and the attached drawings on which, by way of example, onlythe preferred embodimentsof this invention are illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a plan view of oneembodiment of. a system for determining the rate of change of pressure.1

FIG. 2 is a plan view of a vent-type proportional fluid amplifier. a

. FIG. 3 is a plan view of another embodiment of a system for measuringthe rate of change of pressure.

FIG. 4 represents several graphs illustrating the pressure I conditionsof the system of this invention/ n l i.

DETAILED DESCRIPTION By the term fluid as used herein is meant anycompressible fluid such as air, nitrogen, or other gases orincompressible fluid such as water or the like, which fluids may containsolid particles. This invention is not limited to any particular fluid.FIG. 1 illustrates one embodiment of a system embodying an open circuitfor determining the rate of change of pressure including a centerdump-type proportional fluid amplifier 10. Such a proportional fluidamplifier is one wherein the power stream emitted from power nozzle 12is directed to one or the other of outlet passage 14 and 15 or thecenter vent or dump passage 16 in proportion to the magnitude of thefluid control signals applied to control nozzles 18 and 20. Entrainmentfluid flow and venting of excess fluids is accomplished by means ofpassage 22 which is opened to ambient. Control nozzle 18 of proportionalfluid amplifier 10 is connected to a source of pressure within chamber24 by means of passage 26, while control nozzle 20 is connected to thissame pressure source by means of passage 28. For reasonshereinafterexplained, the length of passage 28 is greater than the length ofpassage 26. The outlets l4 and 15 of proportional fluid amplifier 10 areconnected to suitable pressure sensing means, not shown, such as agauge, meter, alarm, Schmitt Trigger, and the like. One familiar withthe art can readily select suitable pressure sensing means for aparticular application.

The operation of the system illustrated in FIG. I is as fol-v lows. Asthe pressure within chamber 24 changes, the pressure P at point Alocated at the intersection of passage 26 and chamber 24 at any giventime will be where L, is the distance between points A and B, and c isthe speed of sound at ambient The equation representing the pressure Pat point C, the entrance to control nozzle 18 of the proportional fluidamplifier, is J L99 Pc Lg/e dt where L is the length of passage 26between points A and- C. Reference is also made to'FIGS. 4(e) and 40).The pressure P at any given time at point D, the entrance to controlnozzle 20, is represented by the equation PD Iii/c dt where L, is thedistance between points A and D" through chamber 24 and passage 28. Thisis also ,illustrated by FIGS.

4(g) and 4(h). The distance between points B and D is L,-, so thatReferringnow additionally to FIG. 4(i), AP, the pressure difference atthe inlet to the proportional fluid amplifier at points C and D isrepresented by the equation AP,=P P,, Substituting equations (3) and (4)in equation (6) (7) JF dP J gPn AP we at (it Ill/c d d dP' K Constant) Ithen The pressure difference AP at outlets l4 and 15 of the proportionalfluid amplifier 10 is represented by the equation (11) AP,.=G1 ARi..

where Gp is the gain of the proport onal fluid amplifier. Substitutingequation (10) in equation (11) (12) APO=GPK gLil-Lz) Thepressuredifference AP at outlets l4 and of the pro- The pressure difference A P,at the outlets of the proportional fluid amplifier is a function of thefirst derivative of the pressure difference at the inlet to saidamplifier or a rate of change of pressure of the pressure source.Equation (12) is suitable for use where L,/c is less than the time ittakes for the pressure to build up within container 24. As heretoforenoted, L must be greater than L The system described above is suitableas a means for detecting the stall condition of a jet engine. Forexample, if chamber 24 is connected at the inlet to a jet engine, theengine stall condition can be detected by sensing the pressuredifferential at the outlet of proportional fluid amplifier whichpressure differential will be a function of the rate of change ofpressure at the engine inlet. As is well known in the art, apredetermined pressure change rate will occur at the inlet to the enginewhen it stalls. In a typical example, a 10 p.s.i. per second rate ofpressure change at stall producing a total pressure rise at the inlet ofa jet engine of 0.02 p.s.i. can be detected by the proportional fluidamplifier connected to the engine inlet as heretofore described. Theoutlets of the amplifier can be connected to, for example, an alarmsystem or an engine shutofi system. With a proportional fluid amplifierhaving a gain of l00:l and where L, is 12 inches and L is 1 inch, A P,would be about I p.s.i.

Referring to FIG. 2 there is illustrated a vent-type proportional fluidamplifier 30. Such a proportional fluid amplifier is one wherein thepower stream emitted from nozzle 32 is directed to one or the other orboth of the outlet passages 34 in proportion to the magnitude of thefluid signals applied to the control nozzles 36. Entrainment fluid flowand venting of excess fluids is accomplished by means of vents 38.

Referring now to FIG. 3, another embodiment of the present system fordetermining the rate of change of pressure is illustrated. A singleconnection is made at point A to a suitable chamber 24 which provides apressure source. One control noule of proportional fluid amplifier 40 isconnected by means of passage 42 to chamber 24. The length of thispassage between points A and C is equal to L in equation (12). The othercontrol nozzle of proportional fluid amplifier 40 is connected by meansof passage to chamber 24 through an intermediate connection to passage42 at point B. The pressure at points C and D is represented byequations (3) and (4) respectively'wherein L is the length of passageABD or the distance between points A and D through assage 44 and L isthe length of passage 42. The operation of INS system Identical withthat described in connection with FIG. 1 in that the pressure difierenceat the outlets of proportional fluid amplifier 40, an analogue device,is a function of the first derivative or rate of change of pressure ofthe, pressure source as sensed at the control nozzles of theproportional fluid amplifier.

I claim:

l. A system for determining the rate of change of pressure comprising:

a proportional fluid amplifier having a power stream nozzle,

a pair of control nozzles, and a pair of outlets;

a pressure source;

a first passage intermediate said pressure source and one of saidcontrol nozzles to transmit fluid from said pressure source to said oneof said control nozzles; and

a second passage intermediate said pressure source and the other of saidcontrol nozzles to transmit fluid from said pressure source to saidother of said control nozzles, said second passage being longer thansaid first passage, the pressure difference A P, at said outlets of saidproportional fluid amplifier being a function of the rate of change ofpressure at said pressure source in accordance with the equation where0,. is proportional fluid amplifier gain, K dP/dl, L, is the length ofthe second passage, L is the length of the first passage, and c is thespeed of sound.

2. The system of claim 1 further comprising pressure sensing meansconnected to the outlets of said proportional fluid amplifier.

3. The system of claim 2 wherein said means is a gauge.

4. The system of claim-1 wherein said first and second passages areconnected to said pressure source at the same point.

5. The system of claim 4 further comprising pressure sensing meansconnected to the outlets of said proportional fluid amplifier.

6. The system of claim 1 wherein said first and second passages areconnected to said pressure source at difi'erent spaced points.

7. The system of claim 6 further comprising pressure sensing meansconnected to the outlets of said proportional fluid amplifier.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3:55 aDated January 12, 1971 Inventor(s) Robert H. Bpl "Iman It is certifiedthat error appears in the aboveidentified patent and that said LettersPatent are hereby corrected as shown below:

Col. 1, line 1?, insert -streambetween "power" and "locks".

Abstract line 10 in the equation (I L should be (L L Col. 2, line 12"passage" should be --passages-.

Col. 3, delete lines 7 through 16. This is a duplicate of lines 18through 25.

Signed and sealed this 13th day of April 1971.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR

EDWARD M.'FLETCHER,JR.

Commissioner of Patents Attesting Officer Prune. nnilnlfl l1n c.o\uscOMM DC. 003 I

1. A system for determining the rate of change of pressure comprising: aproportional fluid amplifier having a power stream nozzle, a pair ofcontrol nozzles, and a pair of outlets; a pressure source; a firstpassage intermediate said pressure source and one of said controlnozzles to transmit fluid from said pressure source to said one of saidcontrol nozzles; and a second passage intermediate said pressure sourceand the other of said control nozzles to transmit fluid from saidpressure source to said other of said control nozzles, said secondpassage being longer than said first passage, the pressure differenceDelta Po at said outlets of said proportional fluid amplifier being afunction of the rate of change of pressure at said pressure source inaccordance with the equation
 2. The system of claim 1 further comprisingpressure sensing means connected to the outlets of said proportionalfluid amplifier.
 3. The system of claim 2 wherein said means is a gauge.4. The system of claim 1 wherein said first and second passages areconnected to said pressure source at the same point.
 5. The system ofclaim 4 further comprising pressure sensing means connected to theoutlets of said proportional fluid amplifier.
 6. The system of claim 1wherein said first and second passages are connected to said pressuresource at different spaced points.
 7. The system of claim 6 furthercomprising pressure sensing means connected to the outlets of saidproportional fluid amplifier.